Isocurvature cosmological perturbations and the CMB

We present a short review on cosmological isocurvature perturbations, which some early universe models predict in addition to the standard adiabatic perturbation. After defining the isocurvature perturbations, we analyse their evolution within the framework of the standard perturbation theory. We then explain how these perturbations can be constrained by the CMB data. We finally discuss some mechanisms that generate isocurvature perturbations. To cite this article: D. Langlois, C. R. Physique 4 (2003).